Soft and calcified tissue implants

ABSTRACT

Disclosed herein is processed dermis graft for use in orthopedic surgical procedures. Specifically exemplified herein is a processed dermis graft comprising one or more bone blocks having a groove cut into the surface thereof, wherein said groove is sufficient to accommodate a fixation screw. Also disclosed is a method of processing dermis that results in a dermis derived implant suitable to replace a tendon or ligament in a recipient in need thereof. Other compositions and applications of a dermis derived implant, and methods of manufacture and use, are disclosed.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.60/296,530, filed on Jun. 6, 2001, and a continuation of U.S.application Ser. No. 09/481,319, filed on Jan. 11, 2000, and acontinuation of U.S. application Ser. No. 09/750,192, filed Dec. 28,2000, and a continuation of U.S. application Ser. No. 09/782,594, filedFeb. 12, 2001, which itself is a continuation of U.S. application Ser.No. 60/181,622. The benefit of priority under 35 USC 119, 120 is claimedfor the foregoing applications, and are also incorporated by reference.

BACKGROUND OF THE INVENTION

Orthopedic medicine is increasingly becoming aware of the vast potentialand advantages of using grafts made from allograft bone to treat andrepair spinal and common joint injuries, such as Anterior CruciateLigament (ACL) or Posterior Cruciate Ligament (PCL) tears. In the caseof injuries involves surgically reconnecting the torn portions of adamaged ligament. However, this technique is often not possible,especially when the damage to the ligament is extensive. The recentutilization of bone/tendon grafts has dramatically improved the resultsof joint repair in cases of severe trauma. Even in cases of extensivedamage to the joint ligaments, orthopedic surgeons have been able toachieve 100 percent range of motion and stability using donorbone/tendon grafts.

Despite these realized advantages, there have been some difficultiesencountered with utilizing bone/tendon grafts. For example, surgicalprocedures involving transplantation and fixation of these grafts can betedious and lengthy. Currently, bone/tendon/bone grafts must bespecifically shaped for the recipient during surgery, which can requirethirty minutes to over an hour of time. Further, surgeons must establisha means of attaching the graft, which also takes up valuable surgerytime.

Another difficulty associated with using allograft implants, such asbone/tendon grafts, is that there is only a limited supply of sourcetissue. As a result, patients often have to settle for inferior surgicalprocedures simply based on the lack of availability of tissue.Accordingly, there is a need in the art for the development of implantsthat implement unrealized sources of tissue.

SUMMARY OF THE INVENTION

One aspect of the subject invention concerns methods of production andcompositions for a novel dermis-derived graft (DDG) that facilitates aneasier and more efficient surgery for reconstructing ligaments in ajoint. While the embodiments herein exemplify the use of dermis tissue,it is understood that other tissue types can be adapted for use inaccord with the teachings herein. Specifically, other soft tissues canbe used such as ligament, tendon, muscle, dura, pericardium, fascia, andperitoneum, as well as demineralized bone. Tissues can be derived fromallogenic, autogenic, or xenogenic sources. Alternatively syntheticmaterials may be used alone or in combination with natural materials. Inone embodiment, the subject invention pertains to a DDG that comprises asection of processed dermis that is rolled to a cylindrical shape, andtwo bone blocks positioned at opposite ends of the rolled dermis,wherein the bone blocks are pre-shaped for uniform and consistentalignment into a recipient bone.

In a specific aspect, the subject invention pertains to a dermis derivedbone-ended graft useful in orthopedic surgery comprising one or morebone blocks, and processed dermis attached to said one or more boneblocks; wherein said one or more bone blocks is cut to provide a groovesufficient to accommodate a fixation screw. Alternatively, the subjectinvention pertains to a dermis derived bone-ended graft useful inorthopedic surgery comprising one or more bone blocks and processeddermis attached to said one or more bone blocks, wherein said one ormore bone blocks is pre-shaped into a dowel.

Another aspect of the invention regards a process for calcification ofall or part of a dermis implant. Comparative data are provided that showthe relative performance of processed dermis implants in laboratoryrats, in which dermis implants had been calcified prior to implantation.

Another aspect of the invention regards the calcification of all or partof a tissue selected from: soft tissue; pericardium; fascia; woven softtissue (as from skeletal muscle); urinary bladder membrane (UBM); andSIS.

Another aspect of the invention is the use of processed dermis as areplacement or as auxiliary support for the Anterior LongitudinalLigament (ALL), and for use as a Spinal Tension Band (STB) or other typeof tension band. For the ALL and STB, the dermis is formed into a shapethat spans the anterior of at least two vertebrae (for an ALL supportstructure) or at least four vertebrae (for an STB), and the ends areaffixed to a part of the vertebrae. The preferred attachment points foran STB are at the spinous processes of the adjacent vertebrae. Thisminimizes movement of (and thereby reduces degradation of) of thevertebrae adjacent to the vertebrae that are being fused. Such adjacentvertebrae are known to undergo excessive wear due to the lack of motionof the adjacent fused vertebrae. The ALL- and STB-type DDGs providetensioning to help prevent excessive back bending due to the partial ortotal functional loss of the ALL owing to surgery or traumatic injury.As disclosed herein, the ends of dermis for such use preferably arecalcified, and starting materials other than dermis may be used for suchapplications.

Preferably, the dermis is processed according to a method that preservesthe dermis basement membrane. A process known to accomplish this is thesubject of U.S. Patent Application Ser. No. 60/296,530, which isincorporated by reference. In yet another aspect, the subject inventionpertains to a method of conducting orthopedic surgery on an animalcomprising obtaining a dermis derived bone-ended graft, said graftcomprising processed dermis having two ends, and one or more bone blocksattached to said processed dermis, wherein at least one of said one ormore bone blocks has a groove suitable for accommodating a fixationscrew.

An alternative aspect of the invention pertains to an implant comprisinga bone block and processed dermis, wherein the bone block comprises agroove for accommodating a fixation screw.

These and other advantageous aspects of the subject invention aredescribed in further detail below.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows diagrams depicting different shapes and constructions of animplant in accordance with the subject invention. FIG. 1A shows abone-tendon-bone type implant. FIGS. 1B-E represent an implantcomprising a specific assembled bone block.

FIG. 2 is a diagram depicting implant embodiments in accord with theteachings herein.

FIG. 3 depicts a first embodiment FIG. 3A and depicts a secondembodiment FIG. 3B of an anterior longitudinal replacement for limitingmotion between adjacent vertebrae to be fused.

FIG. 4 depicts a band for limiting the motion and reducing thedegradation of vertebrae juxtaposed to vertebrae undergoing spinalfusion (i.e., as a spinal tension band) or for being affixed to anyother anatomical structures to minimize motion of such structures inrelation to each other.

FIG. 5 shows plan and perspective views of a bone fixation plug thatcompresses the soft tissue graft component of the implant as the plug isbeing tightened into a hole.

DETAILED DISCLOSURE OF THE INVENTION

The present invention uses processed dermis as a material for implantswhich can be used as replacement or reinforcing tendons, ligaments, andthe like. Particular features of the methods and the products of thepresent invention provide for a dermis-based implant that remodels intoa ‘new’ replacement tendon or ligament. The present invention alsodiscloses a process for the calcification of dermis and other tissues,including soft tissue, pericardium, fascia, woven soft tissue (as fromskeletal muscle), urinary bladder membrane (UBM), and SIS. Thesecollectively are referred to as “implant material,” and when processed,as “processed implant material.” The bone that is used in thisapplication, for instance to comprise bone blocks, may be selected fromcortical, cancellous, cortico-cancellous, or demineralized bone,obtained from human or xenograft sources. Optionally, synthetic materialmay be incorporated in combination with such bone. Also, bone blocks maybe comprised of two or more segments assembled together in a assembledallograft implant. The construction and use of assembled allograftimplants is disclosed more fully in U.S. patent application Ser. No.09/782,594, which is incorporated by reference.

Other features provide for implants fabricated for specificapplications, such as to supplement or replace the anterior longitudinalligament of the spine. Methods of initial preparation and production ofdermis implants, and of specific production for use as ALL- and STB-typeimplants are also disclosed.

I. Preparation of Dermis Derived Graft Material

For the purposes of this disclosure, the term “tendon”, unless otherwiseindicated, is taken to mean flexible fibrous connective tissue thatattaches muscle to bone. In the context of bone/tendon/bone grafts,tendon can refer to the fibrous connective tissue that connects thepatella to the femur and tibia. The term “ligament” is taken to mean themore general term of any fibrous structure connecting one body part toanother, and more particularly to flexible, e fibrous connective tissuethat connects bone to bone or holds organs in place. Also, the term“processed dermis” is taken to mean dermis that has been processed bythe initial processing described herein, or another method ofdecellularizing dermis, and by the secondary process described herein,in which the initially processed dermis is formed into an implant. Adermis derived graft (DDG) is synonymous with a dermis derived implant,and these terms are defined to indicate a graft or implant substantiallycomprised of processed dermis.

The term “processed dermis” as used herein is intended in a broad senseand refers to fibrous connective tissue for use in grafts derived fromdermis of a donor, or from dermis cultured in vitro. The preferredinitial processing is that described in U.S. Patent Application Ser. No.60/296,530, which is incorporated by reference. The initial processingprovides a decellularized dermis sample that retains the structuralfunctionality of the basement membrane. This results in superiorstructural and functional properties of the final dermis derivedimplant.

Basic steps of a preferred initial processing method are summarized asfollows:

-   -   1. Contacting the donor dermis with a viral inactivating agent        that includes benzalkonium chloride; and    -   2. Contacting the dermis with one or more decellularizing        agents, for instance about 0.5 percent Tween 20 and about 0.5        percent hydrogen peroxide.        Additional possible steps include contacting the dermis with        calcium hydroxide (to aid in virus inactivation), with a        chelating agent, for instance EDTA, sonicating the dermis during        such treatments, and drying the dermis, such as by        freeze-drying.

Preferably, a method in accordance with U.S. Patent Application No.60/296,530 is used for initial preparation of the dermis. For example,dermis is selected that is at least 0.7 mm thick, and is free ofepidermis, muscle, fat, hair, scars, moles, debris and tattoos. Thedermis is cut to a desired size, and is soaked in 1 M NaCl. Thereafterthe dermis is soaked in a 1% solution of benzalkonium chloride at 2-6degrees Centigrade for 1-24 hours to reduce microbial load. Then thedermis is immersed in a solution of 1% Tween 20 and 0.5% hydrogenperoxide, and is sonicated for approximately 15 minutes at roomtemperature, stirring at least once per minute. Preferably, microbialload is further reduced by soaking in saturated calcium hydroxidesolution while sonicating for approximately 15 minutes. The dermis isrinsed in purified water to remove the calcium hydroxide,

Thereafter the calcium in the dermis is chelated with EDTA by soaking ina 0.1% EDTA solution for about 15 minutes, and stirring or sonicating.After two rinses to remove the EDTA, the dermis pH is neutralized withbuffer. Then purified water rinses remove the buffer. Drying is begunwith soaking in 70% isopropanol, and is completed with freeze-drying. Ingeneral, the volume of solution to dermis is at least tenfold. This orsimilar initial processing provides dermis ready for further specificprocessing of the present invention.

In one specific, detailed initial processing procedure, the followingsteps are used:

-   -   1. Wash dermis obtained from donor(s) in sodium monophosphate        buffer, pH=7.0, and transfer to a bottle containing a one        percent BZK (benzalkonium chloride) solution. Store by freezing.    -   2. Thaw dermis and transfer to a 1 Molar NaCl solution and        incubate overnight at room temperature. This separates the        epidermis.    -   3. Remove the epidermis and rinse dermis in sterile deionized        water. Cut into desired sizes as needed.    -   4. Place dermis into a 0.5% hydrogen peroxide solution and        sonicate for 15 minutes at room temperature. All dermis must be        covered with the solution during this step.    -   5. Transfer the dermis to a solution (in excess relative to the        dermis sample) of any of the following: 0.5% Tween-20; 0.5%        sodium dodecyl sulfate; 1.0% Triton X-100. Then sonicate for 15        minutes at room temperature.    -   6. Transfer dermis to an excess solution (relative to dermis        sample) of saturated, filtered CaOH. Then sonicate for 15        minutes at room temperature.    -   7. Rinse twice with de-ionized water, then transfer to an        approximately 0.1% EDTA solution, let soak for 15 minutes, then        rinse twice with de-ionized water.    -   8. Rinse dermis sample(s) in an excess solution of sodium        monophosphate buffer (pH=7.0) three times, for five minutes each        time.    -   9. Rinse dermis sample(s) in sterile deionized water.    -   10. Transfer dermis sample(s) to an excess of 70% isopropyl        alcohol for 15 minutes to dehydrate the dermis (do not        sonicate).    -   11. Package dermis, or cut to size (if not already cut), and        package for lyophilization.    -   12. Lyophilize the sample(s).    -   13. Treat dermis with a low dose of gamma radiation.

After initial processing, in certain applications the dermis is furtherprocessed to form, as described in section III, implant structuressuitable for use as a tendon or ligament. Alternately, the dermis isused for other types of implants, including those referred to in sectionIV below.

The major component of the processed dermis is collagen. A cross linkingstep may be added in the initial processing, or in the subsequentprocessing where the implant is being formed or shaped (such as insection II), to cross link collagen molecules. Cross linking approacheshave been described in a previous application for a moldable bone paste,U.S. application Ser. No. 09/750,192, which is incorporated byreference, and is described here for the present application.

Typical chemical cross-linking agents used in accord with this inventioninclude those that contain bifunctional or multifunctional reactivegroups, and which react with collagen of the processed dermis. Byreacting with multiple functional groups on the same or differentcollagen molecules, the chemical cross-linking agent increases themechanical strength of the implant.

The cross-linking step of the subject embodiment involves treatment ofthe dermis to a treatment sufficient to effectuate chemical linkagesbetween adjacent molecules. Typically, such linkages are betweenadjacent collagen molecules exposed on the surface of the dermis.Crosslinking conditions include an appropriate pH and temperature, andtimes ranging from minutes to days, depending upon the level ofcrosslinking desired, and the activity of the chemical crosslinkingagent. Preferably, the implant is then washed to remove all leachabletraces of the chemical.

Suitable chemical cross linking agents include mono- and dialdehydes,including glutaraldehyde and formaldehyde; polyepoxy compounds such asglycerol polyglycidyl ethers, polyethylene glycol diglycidyl ethers andother polyepoxy and diepoxy glycidyl ethers; tanning agents includingpolyvalent metallic oxides such as titanium dioxide, chromium dioxide,aluminum dioxide, zirconium salt, as well as organic tannins and otherphenolic oxides derived from plants; chemicals for esterification orcarboxyl groups followed by reaction with hydrazide to form activatedacyl azide functionalities in the collagen; dicyclohexyl carbodiimideand its derivatives as well as heterobifunctional crosslinking agents;hexamethylene diisocyante; sugars, including glucose, will also crosslink collagen.

It is known that certain chemical cross-linking agents, e.g.,glutaraldehyde, have a propensity to exceed desired calcification ofcross-linked, implanted biomaterials. In order to control thiscalcification, certain agents can be added into the composition of thesubject embodiment, such as dimethyl sulfoxide (DMSO), surfactants,diphosphonates, aminooleic acid, and metallic ions, for example ions ofiron and aluminum. The concentrations of these calcification-temperingagents can be determined y routine experimentation by those skilled inthe art.

When enzymatic cross-linking treatment is employed, useful enzymesinclude those known in the art which are capable of catalyzingcrosslinking reactions on proteins or peptides, preferably collagenmolecules, e.g., transglutaminase as described in Jurgensen et al., TheJournal of Bone and Joint Surgery, 79-a(2), 185-193 (1997), hereinincorporated by reference.

Formation of chemical linkages can also be accomplished by theapplication of energy. One way to form chemical linkages by applicationof energy is to use methods known to form highly reactive oxygen ionsgenerated from atmospheric gas, which in turn, promote oxygen crosslinks between surface-exposed collagen. Such methods include usingenergy in the form of ultraviolet light, microwave energy and the like.Another method utilizing the application of energy is a process known asdye-mediated photo-oxidation in which a chemical dye under the action ofvisible light is used to cross link surface-exposed collagen.

Another method for the formation of chemical linkages is bydehydrothermal treatment which uses combined heat and the slow removalof water, preferably under vacuum, to achieve crosslinking of collagenin the processed dermis. The process involves chemically combining ahydroxy group from a functional group of one collagen molecule and ahydrogen ion from a functional group of another collagen moleculereacting to form water which is then removed resulting in the formationof a bond between the collagen molecules.

II. Preparation of Calcified Dermis Derived Implant

It has been learned that the ends, other sections of, or an entire pieceof the processed dermis, may be calcified by the following process. Bymodifying the twelve-step method shown above, such that the contactingwith calcium hydroxide solution is followed immediately by the phosphatebuffer solution, calcium is deposited onto (or precipitates onto) thedermis. Approaches to calcifying the dermis sample include contactingwith the phosphate buffer slowly, as by changing out the solution inwhich the dermis section is held, or rapidly, as by moving the dermissection from a vessel containing the calcium hydroxide to a vesselcontaining phosphate buffer. The preferred pH of the phosphate buffer isin the range of 6.8 to 7.2 pH units. While not being bound to aparticular theory, the change in pH is believed to cause a precipitationof calcium onto the processed dermis. The deposited calcium addsrigidity to the section. It has been observed that calcification willnot occur appreciably if the EDTA solution is used between the calciumhydroxide step and the phosphate buffer step. The following evaluationillustrates one use of calcified dermis prepared according to thisinvention.

Evaluation of Initially Prepared Dermis in Animal Model

Samples of dermis were prepared using the twelve-step method describedin section I, varying the type and amount of detergent agent, as shownin the table of results.

Thereafter, the dermis so prepared was implanted and evaluated asdescribed below.

A. Sample Preparation for Implantation

1.) Lyophilized dermis was cut (aseptically) into approximately 1×1 cmimplants, weighed before hydration (pre-implantation dry weight), andrehydrated with sterile saline containing antibiotics.

-   -   2.) Samples were implanted (4 per rat) into Athymic nude rat        model following SOP# with modification: only one suture was used        to hold the implant in place.    -   3.) Implants were recovered at 3, 6, and 12 week        post-implantation (2 week samples per donor/per treatment/per        time point−total of 6 for each treatment/time point) 1-2 were        kept for historical analysis and 4-5 were removed, lyophilized        to determine dry-weight post-implantation (to determine percent        loss of tissue after in vivo exposure).        B. Animal Surgeries

1.) Surgeries were performed as follows: Animals were anesthetized viaintramuscular injection (thigh or gluteus muscle) of ketamine (100 mg/k)and Xylazine (15 mg/kg). Sterile technique was used and surgery wasperformed in a class 100 hood. Alcohol and providone iodine were appliedto the abdomen of the animal. An incision was made parallel to themidline of the abdomen from just below the tip of the sternum to justabove the navel. The skin is dissected away from the underlying muscleon either side of the abdomen. The muscle is isolated and a 0.5×0.5 cmarea of fascia was scored from the muscle until the muscle bled, one arein each quadrant of the abdomen. A 1×1 cm piece of dermis was sutured tothe muscle over the area that was previously scored, with two corners ofthe dermis sutured in to place with non-absorbable 3-O prolyene suture.The skin was closed with wound clips in a continuous line. Providoneiodine is reapplied to the wound and the animal is returned to its' cageaccording to (Rat Assay Osteoinductivity Surgery) with the followingexceptions:

2.) At 3, 6, and 12 weeks, animals were sacrificed according to a humaneprocedure.

3.) The skin was shaved on the stomach using a disposable razor or hairclippers.

4.) The muscle flap with the overlying skin was removed.

5.) The entire muscle flap was photographed for macroscopic observation.

6.) Implant material was removed (6 per time point for each testsample), and placed in labeled sterile petri dishes for drying. Ifimplants were difficult to remove, the entire muscle flap was removedand the implant was carefully excised using scalpels in the lab. Beforedissection, each implant site was photographed for documentationpurposes.

7.) 3 implants of each sample at each time point was prepared forhistological processing. (H&E staining)

C. Results and Discussion Dry Implant Group Implant Weight Dry ExplantWeight % Change 1Fa 40 SDS .0225 .0542 +140.9% 1Ed .0218 .0469 +115.1%1Bd .0236 .0259  +9.7% 1Gd 40 Triton .0121 .0352 +190.9% 1He .0126 .0404+220.6% 2Ad .0086 .0271 +215.1% 1Db 40 Tween .0073 .0231 +216.4% 2Fe.0091 .0309 +239.6% 1Fe .0073 .0289 +295.9% 2Eb 41 SDS .0148 .0370  +150% 1Eb .0107 .0342 +219.6% 1Cb .0104 .0342 +228.8% 2Ee 41 Triton.0068 .0272   +300% 1Gb .0080 .0282 +243.9% 2Be .0077 .0304 +294.8% 2Da41 Tween .0075 .0239 +218.7% 2Ca .0071 .0241 +239.4% 2Aa .0079 .0282  +257% 2Fb 42 SDS .0062 .0207 +233.9% 1Db .0073 .0231 +216.4% 1Ee .0079.0242 +206.3% 1Bd 42 Triton .0096 .0585 +509.4% 1Ce .0111 .0332 +199.1%1Aa .0099 .0322 +225.3% 2Fa 42 Tween .0129 .0446 +245.7% 1Fb .0093 .0290+211.8% 1Dd .0155 .0555 +258.1%

Explants appeared to have calcified during the first four-week period toa low degree. X-Ray analysis confirmed the presence of calcified matrix.This is postulated to be due to neutralization of the CaOH treatmentwith buffer which resulted in the precipitation of calcium phosphate onthe tissue. When calcification of the dermis is not desired, the dermiscan be thoroughly washed with sterile water and EDTA prior toneutralization with buffer.

These results show an increased level of bone deposition that isbelieved related to the initial levels of calcification described inthis section. In vivo the implants became much less pliable compared toimplants processed in a standard, non-calcifying manner. The inventorsbelieve that in some applications, some forms of calcified, processeddermis implants could form bone. This is based on the fact that bothdemineralized bone (which forms bone as an implant) and acellular dermisare comprised of primarily Type I collagen

In addition, growth and other factors, as are known in the art andadministered to suit the purpose of the particular application, areadded to the implant. For example, prior to assembly or after assembly,the graft materials are soaked, infused, impregnated, coated orotherwise treated with bone morphogenetic proteins (BMP's), antibiotics,growth factors (including angiogenic growth factors), nucleic acids,peptides, and the like.

It is noted that all or part of other tissue samples, whether allograft,xenograft or autograft, may be calcified in accordance with the presentinvention. Examples of such tissues include: soft tissue; pericardium;fascia; woven soft tissue (as from skeletal muscle); urinary bladdermembrane (UBM); and SIS. Accordingly, where the term DDG is used inregard to calcification, it is appreciated that these tissue types maybe substituted for the dermis tissue. Variations in the duration of aparticular step, and other modifications of the above describedprocesses, may be required to optimize the process for each such tissue.However, such modifications are within the scope of reasonableexperimentation having the above process as guidance.

III. Production of Dermis-Derived and Other Types ofTendon/Ligament-Type Implants

Dermis processed as described above, or as processed by other methods,can be fabricated into an implant that substitutes for or replaces atendon or ligament in a recipient in need thereof. The dermis derivedimplant may be used as a scaffold for tendon and ligament regeneration,a locus for remodeling that is superior to other implant choices (e.g.,demineralized ligament, urinary bladder matrix, small intestinesubmucosa). While not being bound to a particular theory, this isbelieved due to the presence of a collagen structure that is less labileto enzymatic degradation than other implant choices, and to the presenceof the basement membrane. However, it is understood that other materialsmay be utilized in accord with the teachings herein, including but notlimited to, demineralized bone (partially or fully), ligaments, tendons,peritoneum, urinary bladder matrix, dura mater, and muscle, fromallograft and xenograft sources.

The following embodiments of implants and their production are meant tobe illustrative, and not limiting. It is noted that for the followingembodiments, the processed dermis is a material suited for remodeling bythe recipient's body into a ‘new’ tendon or ligament.

Thus, one aspect of the present invention is processing dermis forspecific use as a tendon implant. For example, a section of dermisinitially processed by the method described in section I isreconstituted by soaking in a 5% gelatin solution for two minutes. Thesection is rolled around a wooden swab to establish a desired thicknessand mass for the intended application. One end, approximately ½ inch, ofthe rolled dermis is immersed in a saturated calcium hydroxide solution,and this is sonicated for 10 minutes. The dermis is soaked in 50 mMphosphate buffer for 10 minutes, and soaked in acetone for 30 minutesfor initial drying. Drying is continued with placement in a drying ovenset to approximately 60 degrees Centigrade for two hours.

Following the above procedure, in one trial it was observed that thelayers of the dermis, upon subsequent reconstitution, slightly separatedin some places.

In a subsequent trial, the dermis was soaked in gelatin as above, rolledaround the swab mandrel and secured with suture material. Then this waswrapped in a paper towel and rolled under pressure. This was frozen, andthen freeze-dried. The step of soaking in acetone was excluded. Thedermis so processed was more difficult to separate compared to the firsttrial's samples. It was determined in animal trials that the implantonly needs to hold together during surgery because proper fixation atthe ends will ensure that the implant functions.

Typical embodiments of dermis-derived tendons and ligaments comprise amain intermediate section of processed dermis and two ends forattachment of the implant to desired body parts of a recipient. In oneembodiment, one or more soft tissue screws are used to attach each endto a desired body part. In another embodiment, one or both ends arefixed in a substance (for instance, alpha-BSM, hydroxyapatite, calciumsulfate) which hardens the end(s) and allows the use of a hard tissueinterference screw for attachment to the recipient's body part. This isdescribed in section II. Alternately, as described below, the ends areattached to pieces of bone that are suited for subsequent attachment tothe recipient's body part.

In addition to the above basic steps, the dermis may be cross linked,such as by the methods and agents described in section I. Alternately,or in addition, an appropriate biocompatible adhesive may be added toattach the outer flap to the immediately underlying layer. Alternately,or in addition, the dermis is held together and on the swab (or othermandrel-like device) with string, twine, suture material, or otherwrapping. Pressure is applied as needed to help hold the rolled layerstogether. Layering the dermis provides additional strength, and crosslinking the layers further adds to the strength.

In addition, growth and other factors, as are known in the art andadministered to suit the purpose of the particular application, areadded to the implant. For example, prior to assembly or after assembly,the graft materials are soaked, infused, impregnated, coated orotherwise treated with antibiotics, growth factors (including angiogenicgrowth factors), nucleic acids, peptides, and the like.

Regarding the use of pieces of bones at one or more ends of theprocessed dermis, referring to FIG. 1A, there is shown an embodimentdirected to a DDG 100 comprising a first bone block 110 and a secondbone block 120 interconnected by processed dermis 130, in which the boneblocks have been pre-shaped into dowels.

To facilitate placement of a fixation screw, dowels are preferablymachined down the length of the bone block to form radius cuts 115, 125.The radius cuts 115, 125 aid in the attachment of the graft to recipientbone because they provide a groove to position a fixation screw, whichresults in increased surface area at the contact between the bone blockand the screw. The radius cuts 115, 125 provide the additional advantageof increasing the pull out loads of the bone block, as well as fillingof dead space in tunnel.

Fixation methods known in the art can be used in accord with theprinciples of the subject invention, which include, but are not limitedto, staples, buttons, screw and washer, interference screws, andself-taping screws. In a preferred embodiment, fixation is accomplishedby interference screws and/or self-tapping screws. In an even morepreferred embodiment, the radius cuts 115, 125 contain a thread profile135 that matches the thread profile of the fixation screw, therebyfurther increasing the stability of fixation.

Referring to FIG. 1B-C, another embodiment directed to an implant 150that employs a bone block, 151 that comprises a ‘tee-’ or ‘cross-’shaped profile. The bone block is comprised of two interlockingsubstantially planar pieces, 151 a and 151 b, that comprise a slot 163and slip together to present four fins, 152 a-d, that radiate from acenter point, 154. The substantially planar segments comprise a slot 163that defines a slotted section 165 and a body section 166. The preferredlength of the bone block, 151, is approximately 2.5 mm, and thepreferred diameter may range from approximately 2.0 to 12.0 mm.

Processed soft tissue is attached to the bone blocks by variousconventional means known to those skilled in the art, as describedbelow. In addition, the processed soft tissue is attached by wrappingthrough holes made in the fins, 152 a-d, of the bone block 151. As shownin FIG. 1D, the processed soft tissue 153 also can be passed into onechannel and out a second channel and then fastened to form a loop (as bysutures, tying, etc.). In a preferred embodiment (shown in FIG. 1C), twoseparate flexible bands 161 and 162 (natural, e.g., dermis or synthetic)are looped over the top of the bone block 151, wherein one band 162contacts fins 152 a and c, and the second band 161 contacts fins 152 band d. When the bone block 151 is positioned into a channel, such as atunnel formed in a patient's bone during surgery, the two bands loopedover the bone block 151 are compressed against the fins 152 a-d andthereby secured into place. Alternatively, the ends of the fins cancomprise teeth or are otherwise irregular to further prevent slippage ofthe bands.

To fasten the tee-shaped bone block to the bone of a recipient in needof an implant, a round hole is drilled into the site of placement. Thebone block is inserted to the desired depth, and at least oneinterference screw, 157 (FIG. 1F) is placed along side the bone block151 and is tightened to set compress the bone block against the wall ofthe hole in the recipient's bone.

It is well recognized that many other shapes of bone blocks, as known orconceived by one of ordinary skill in the art, will serve the purpose ofattachment in the present invention. For instance, a bone block withthree, rather than four fins, in profile, can be used.

Referring now to FIG. 2, three different embodiments of the subject DDGsare shown. FIG. 2A shows an embodiment that comprises a basicconfiguration of the subject DDGs. Bone blocks 210 and 220 are in apre-shaped dowel form with no groove thereon, and are connected byprocessed dermis 100. FIG. 2B shows another version of the DDG, whereinthe bone blocks are pre-shaped into dowels with tapered ends. Bone block212 is a dowel that has a proximal tapered region 216 in relation toprocessed dermis 200, and bone block 214 is pre-shaped into a dowel thathas a distal tapered region 218 in relation to processed dermis 200.FIG. 2C illustrates a preferred version of the invention, which has abone block 230 with a proximal tapered region 239 and a groove 238positioned on the bone block 230. This version also comprises a secondbone block 234 with a distal tapered region and a groove 236 positionedon bone block 234 as well. The embodiments shown in FIGS. 2B-C aretapered such that implantation into a pre-formed tunnel in recipientbone is preferred to occur in the direction of the arrow.

In an alternative embodiment, the subject invention is directed to animplant having at least one bone block portion and at least oneprocessed dermis section, wherein the bone block portion comprises agroove on its exterior. Once the bone blocks are extracted, they aremachined into a dowel or other desired shape. In a specific embodiment,the dowel is machined into dimensions suitable for various surgicalprocedures. The machining is preferably conducted on a graduated die, agrinding wheel, a core cutter, a lathe, or machining tools that arespecifically designed and adapted for this purpose. Preferred dimensionsof the diameter for the dowels include 9 mm, 10 mm, 11 mm, and 12 mm.Reproducibility of the product dimensions is an important feature forthe successful use of such grafts in the clinical setting.

The bone ends, whether in the shape of a dowel, other shapes describedherein, or shapes known to those skilled in the art, are attached to theprocessed dermis by means such as chemical annealing, chemical adhesive,suturing (optionally through drilled holes in the bone), pinning to, orwrapping and tying the processed dermis around the bone ends (andoptionally applying a suitable adhesive). When the attachment meansincludes use of tying the processed dermis to a bone end, the bone endoptionally has grooves transverse to the long axis of the assembly whichmay receive the windings of the wrapping line (suture material or othersuitable line). Furthermore, a block may be used that comprises anassembled block formed from two or more individual segments fastenedtogether. The block made be made from cortical, cancellous bonesegments, or both that are obtained from allogenic, autogenic, orxenogenic sources. The bone segments may be mineralized, or partially orfully demineralized. Furthermore, the block may be made from syntheticsegments or a combination of bone and synthetic segments. Syntheticmaterials contemplated for use herein include, but are not limited to,stainless steel, titanium, cobalt chromium-molybdenum alloy, and aplastic of one or more members selected from the group consisting ofnylon, polycarbonate, polypropylene, polyacetal, polyethylene oxide andits copolymers, polyvinylpyrolidone, polyacrylates, polyesters,polysulfone, polylactide, poly(L-lactide) (PLLA), poly(D,L-lactide)(PLA), poly(glycolide) (PGA), poly(L-lactide-co-D,L-Lactide) (PLLA/PLA),poly(L-lactide-co-glycolide) (PLA/PGA), poly(glocolide-co-trimethylenecarbonate) (PGA/PTMC), polydioxanone (PDS), polycaprolactone (PCL),polyhydroxybutyrate (PHBT), poly(phosphazenes),poly(D,L-lactide-co-caprolactone) (PLA/PCL),poly(glycolide-co-caprolactone) (PGA/PCL), poly(phosphase ester),polyanhydrides, polyvinyl alcohol, hydrophilic polyurethanes, and acombination of one or more bioabsorbable polymers. Copending U.S.application Ser. No. 09/782,594 is incorporated herein by reference fordisclosure on assembled implants.

Another shape of bone block is shown in FIG. 5. A two-part bone fixationplug, or screw, 501, has a first half, 502 and a second half, 503, thatfit together. Each half, 502 and 503, has an outer surface, 520 and 521,respectively, that comprises approximately half of a generally conicalshape. Each half, 502 and 503, has an inner mating surface, 522 and 523,respectively, whose surface generally matches the other side's innermating surface so as to form, when joined together or in closeproximity, a substantially conical surface on the outer surface. Theshape of the inner mating surfaces may be curvilinear, flat, or acombination, or may comprise ridges, grooves, teeth or some otherirregular shape to aid in gripping the soft tissue placed thereon. In apreferred embodiment the inner mating surfaces are substantially flat.

One or both of the inner mating surfaces 522 and 523 have one or moreprotrusions for alignment that, upon mating of the halves 502 and 503,enter matching voids or holes to align the joining together of thehalves, 502 and 503. As shown in FIG. 5, the protrusions may be in theform of pins 524 from a first half, 502, that enter counterposed holes525 in a second half, 503. The end section, 504, of a processed softtissue, 505, such as dermis, is positioned between the inner matingsurfaces, 522 and 523. The ends 530,531 of the plug, 501, preferablyhave driver hole formed therein to receive a driving tool when the twohalves 502,503 are brought together; for instance, a shallow hexagonalcavity for a hex (Allen) wrench, a lateral or ‘tee’ slot for ascrewdriver, the outer border shaped hexagonally to receive an open endwrench or socket, or other means known to those of ordinary skill in theart.

The plug, 501, has threads, 508, on the generally conical outersurfaces, 520 and 521. The threads of the first half, 502, and thesecond half, 503, of the plug, 501, are generally of the same size andare designed to approximately meet when the halves are joined together.When the halves, 502 and 503, are joined together, the plug, 501, isthreaded into a sized hole in a bone of a recipient in need of animplant. As the plug passes farther into the hole, the inner matingsurfaces, 522 and 523, are compressed closer together, and thesecompress against the soft tissue end, 504. This fastens the soft tissue,505, to the bone block.

It is noted that various means to control the compression by and contactwith the inner mating surfaces onto the soft tissue end, 504, can beeffectuated. For instance, spacers or nub on the inner mating surfaces,preferably spaced peripherally to where the soft tissue end contacts,can stop the travel of the inner mating surfaces to provide a sufficientlevel of compression without crushing the soft tissue end, 504. Groovesor ridges on one or both of the inner mating surfaces, 522 and 523, canprovide extra friction and pressure to avoid slippage. These can bealone or in combination with the peripheral spacers or nubs. Otherdesigns can be implemented, where the basic goal is to compress a softtissue graft component of the implant as the plug is being tightenedinto a hole, so the soft tissue component is attached to, or locked intothe plug. For instance, the soft tissue end, 504, may have a thickerbitter end, and this may fit into a depression in one or both innermating surfaces, so that upon compression this thicker end would beunable to slip through the narrower space between the rest of the flatsurfaces. In another embodiment, the end, 504, of the soft tissue, 505,passes entirely through both inner mating surfaces of the plug, 501, soit extends beyond the ends, 530 and 531, of the plug, 501. The end ofthe implant material, 504, may be thickened so it abuts to the endsurface 530, of the plug, 501, or it may be later adjusted and fastened,such as by suturing or tying in a knot.

As shown in FIG. 5E, a variation of this embodiment is to insert thefixation plug, with the long portion of tissue 505 preceding the plug,into a hole 537 that passes entirely through a bone 526 of a recipient.A tapered hole may be used, so the soft tissue component passes from ahole that is relatively small in comparison to the opening into whichthe fixation plug is tightened. As the plug 501 comprising the twohalves 502 and 503 is secured into the hole 537 they compress and securethe soft tissue 505.

The above discussion regards the joining of one end of a section ofimplant material, such as processed dermis, with a bone plug havingvarious characteristics. It is recognized that when a bone-tendon-boneor similar implant is made, it typically has a bone plug at both ends ofthe flexible implant material that functions as a tendon matrix. Aparticular bone-tendon-bone or similar implant may use the same type ofbone plug at both ends, or may use different types of bone plugs at eachend, depending on the structural requirements of the recipient, theavailability of implant parts, and other factors. Also, although theexample in this section regarded processed dermis, it is recognized, asdisclosed in the preceding section, that tissues other than dermis maybe processed and used for bone-tendon-bone and similar implants.

Finally, as noted above, the bone that is used to construct bone blocksmay be selected from cortical, cancellous, cortico-cancellous, ordemineralized bone, obtained from human or xenograft sources.Optionally, synthetic material may be incorporated in combination withsuch bone. Also, bone blocks may be comprised of two or more segmentsassembled together in a assembled allograft implant.

IV. Implants for Augmenting or Replacing the Spinal AnteriorLongitudinal Ligament (ALL) and Other Uses

In another aspect of the invention, a processed dermis implant (DDG) isused to augment or replace the function of the anterior longitudinalligament (ALL), such as after a surgery that partially or completelysevers the ALL (such as during insertion of disc replacement implants orprostheses), or after other damage (e.g., trauma) to the ALL.Preferably, the DDG is calcified at the ends to allow use of strongermeans of attachment. It is noted that, depending on the nature of thesurgery, a disc replacement/spinal fusion operation may access thevertebrae by partially or completely severing the ALL. Without a fullyfunctional ALL, there is a risk of damage to the spine from excessivebackward bending in that the intact ALL tensions the anterior span ofthe spine. Also, the DDG stabilizes the motion of the segmentanteriorly. This is more conducive to spinal fusion.

An additional advantage of a DDG produced according to the method ofthis invention, for the application of augmenting or replacing apartially or completely severed ALL, is that is may block and therebyprevent the expulsion of interbody grafts. Such DDGs are preferablyaffixed to the vertebral bodies with screws, pins, staples or anchors ofvarious types known in the art or heretofore developed. The attachmentmeans preferably are well secured and with means to minimize thepossibility that the attachment means will loosen, as such loosening inthe vertebral area, rich with blood vessels and nerves, can be extremelydangerous and potentially leads to death. One embodiment uses bonescrews which are applied with a bone paste to accelerate bone growthonto the bone screws.

As a result of placing a DDG to span two adjacent vertebrae, lumberextension is reduced, thereby providing a more stable environment topromote fusion. In FIG. 3, there is provided one embodiment 300 of theDDG ALL implant according to this invention. This implant 300 isprepared from processed dermis which has been folded to providesufficient strength. A top portion, 310, and a bottom portion, 320, areprefereably fully mineralized, or partially mineralized, as bycalcification. Also, the mineralization may be restricted to the surfacelayer(s) to modify the stress-fracture behavior of the implant. The topportion 310 and the bottom portion 320 each have a series of holes 305by means of which the DDG implant is affixed to a superior vertebra V1and an inferior vertebra V2. The intermediate section, 330, is processedto maintain a desired degree of flexibility while maintaining sufficienttensional strength. In this fashion, while permitting a slight amount ofmotion, the DDG implant substantially restricts motion at the vertebralsegment spanned by the DDG implant. Also shown in outline is a pair ofinterbody implants 340 inserted between superior vertebra V1 andinferior vertebra V2. In FIG. 3B, there is shown a further embodiment ofthe DDG implant of this invention which is identical in all respects tothe implant shown in FIG. 3A, but wherein this embodiment has anenlarged upper segment 310′ and lower segment 320′ for affixation to thevertebrae V1 and V2. It will be appreciated that the precise shape ofthe DDG implant is not critical. Furthermore, the DDG implant may spanmore than two vertebrae. In one preferred embodiment the DDG implant is20 to 30 mm wide and 3 mm thick, and has one aperture in each of itsfour corners.

In yet a further embodiment of the DDG implant of this invention, thereis provided a spinal tension band, STB. Typically, in spinal fusions,the motion segment adjacent to the fused segment (the juxtaposed discs)have been found to rapidly degrade. This degradation appears to be dueto the hyper motion at these levels, due to the decreased motion at thefused segments. The STB of this invention assists in preventing thisdegradation and can avoid the need for further surgery, by spanning thefused segments and attaching to the juxtaposed vertebral body at thespinous process thereof. The STB may be used in any region of the spine,but is typically most useful for spanning fusions at two, three, or morelevels. The STB of this invention replaces or augments use of flexiblestainless steel, titanium cables, elastomeric or polymeric syntheticmaterials currently in use. Accordingly, known techniques for attachingsuch devices to the spinous processes may be used, or the STB may beaffixed to juxtaposed vertebral bodies in a fashion analogous to thatdescribed above for the DDG implant to augment or replace the ALLfunction.

In FIG. 4, there is disclosed one embodiment of the STB 400 of thisinvention. As can be seen, the STB 400 is affixed to a superiorvertebra, VA, and an inferior vertebra, VB, each of which are juxtaposedto a vertebra V1 and V2, which are being fused to each other by means ofinterbody fusion devices IB1 and IB2. Intermediate portion 410 is dermisprocessed to maintain a desired level of flexibility and strength, whilethe top portion 420 and the bottom portion 430 are preferably in amineralized or partially demineralized state. Affixation means 425 and435 are provided for fixation of the STB to the juxtaposed vertebrae VAand VB, respectively. Those skilled in the art will appreciate that thisembodiment of the invention may be applied to any other anatomicalstructure to minimize motion of such structures in relation to eachother. For example, the tension band of this invention may be utilizedoutside of the spinal context, for example for the repair of a splitsternum in a sternotomy. Also, the tension band of this invention isused for spanning a bone fracture site. In this application, one or moretension bands are attached to attachment sites on both sides of thefracture.

It is further appreciated that other implant substances may be processedand utilized for an implant to augment or replace an ALL or as an STB orother tension band. Among the implant materials that may be used are:segmentally demineralized bone; fascia, pericardium; ligaments; tendons(including as processed as described above, herein); ligaments; muscle;dura; xenograft demineralized bone; xenograft segmentally demineralizedbone; calcified implant materials made from soft tissue, fascia,pericardium, UBM, SIS, or woven soft tissue (skeletal muscle); or anycombination of these implant substances, and optionally in combinationwith biocompatible synthetic materials. Further, as appropriate thesemay be attached to bone pieces (human or xenograft), for instance whenthe bone pieces provide a preferred means of affixation to the bone orother part of the recipient.

It also is noted that strip size variations are recognized and arewithin the scope of this invention. For instance, wide or narrow stripscomprising the ALL, STB, or tension band implants may be used. Also,strips each comprising a layering of dermis, or other allograft tissuessuch as those listed above, may be used at one or two levels (e.g., oneinternal to the other), and the implants may be used for the cervical,thoracic, or lumbar regions of the spine. Further, the implantsdescribed in this invention may be used to augment or replace theposterior longitudinal ligament for procedures where this ligament is inneed of augmenting or replacing.

Those skilled in the art will appreciate that the graft may be anautograft, allograft, or xenograft. Xenograft implants may furtherrequire treatments to minimize the level of antigenic agents and/orpotentially pathogenic agents present in the graft. Techniques nowknown, or those which are later developed, for preparing tissue suchthat it is suitable for and not rejected by the recipient areincorporated herein. In cases where the graft is an allograft, a donoris preferably screened for a wide variety of communicable diseases andpathogens, including human immunodeficiency virus, cytomegalovirushepatitis B, hepatitis C and several other pathogens. These tests may beconducted by any of a number of means conventional in the art,including, but not limited to, ELISA assays, PCR assays, orhemagglutination. Such testing follows the requirements of the followingassociations: (a) American Association of Tissue Banks. Technical Manualfor Tissue Banking, Technical Manual-Musculoskeletal Tissues, pagesM19-M20; (b) The Food and Drug Administration, Interim Rule, FederalRegister, Vol. 58, No. 238, Tuesday, December 14, Rules and Regulations,65517, D. Infectious Disease Testing and Donor Screening; (c) MMWR,Vol.43, No. RR-8, Guidelines for Preventing Transmission of HumanImmunodeficiency Virus Through Transplantation of Human Tissue andOrgans, pages 4-7; (d) Florida Administrative Weekly, Vol. 10, No.34,Aug. 21, 1992, 59A-1.001-014, 59A-1.005(12)(c), F.A.C., (12)(a)-(h),59A-1.005(15, F.A.C., (4) (a)-(8). In addition to a battery of standardbiochemical assays, the donor, or their next of kin can be interviewedto ascertain whether the donor engaged in any of a number of high riskbehaviors such as having multiple sexual partners, suffering fromhemophilia, engaging in intravenous drug use etc. Once a donor has beenascertained to be acceptable, the tissue for obtaining the DDGs asdescribed above are recovered and cleaned.

The teachings of all patents and publications cited throughout thisspecification are incorporated by reference in their entirety to theextent not inconsistent with the teachings herein.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication and the scope of the appended claims.

1-63. (canceled)
 64. A dermis derived bone-ended graft useful inorthopedic surgery comprising at least one assembled bone block and anelongated section of processed dermis attached to said at least one boneblock.
 65. The graft of claim 64, wherein at least one of the at leastone assembled bone block is comprised of cortical, cancellous,cortico-cancellous, or demineralized bone, obtained from human orxenograft sources.
 66. The graft of claim 65, wherein at least one ofthe at least one assembled bone block is comprised of two segments. 67.The graft of claim 66, wherein said two segments are in the shape ofdisks.
 68. A soft tissue implant for spanning two or more vertebrae, orfor spanning a bone fracture site, comprising: a. a middle sectioncapable of flexion and having a first end and an opposing second end; b.a top section attached to the first end of said middle section andcomprising a first assembled bone block having at least one aperture forattaching to a first vertebrae or to a section of bone on a first sideof a fracture, said first assembled bone block comprising two segmentsof cortical bone; and c. a bottom section attached to the second end ofsaid middle section and comprising a second assembled bone block havingat least one aperture for attaching to a second vertebrae or to asection of bone on an opposing side of a fracture, said second assembledbone block comprising two segments of cortical bone.
 69. The soft tissueimplant of claim 68, wherein said middle section comprises dermis,fascia, pericardium, woven soft tissue, urinary bladder matrix,peritoneum, or demineralized bone.
 70. The soft tissue implant of claim68, wherein the first end and the second end of said middle section arecalcified.
 71. The soft tissue implant of claim 68, wherein said topsection and said bottom section comprise allograft bone.
 72. The softtissue implant of claim 68, wherein said top section comprise xenograftbone.
 73. An implant for use as a tension band between vertebrae in apatient in need thereof, comprising a longitudinal device having a topsection, a bottom section, and a middle section, the middle sectionbeing flexible, wherein the top and the bottom sections each comprise anassembled bone block having a plurality of holes that facilitateattachment to a corresponding vertebrae.
 74. The implant of claim 73,wherein said middle section is fabricated from a material selected fromthe group consisting of segmentally demineralized bone, fascia,pericardium, ligament, tendon, muscle, dura, xenograft demineralizedbone, xenograft segmentally demineralized bone and a combinationthereof.